As an investigation continued into the Tuesday fire that was doused within 90 minutes, local activists pointed to the accident as yet another signal that serious intervention is needed to protect the region from a disaster because of the hazardous chemicals used at the Torrance Refining Co. plant

“This particular accident ended without catastrophe and without spreading,” said Sally Hayati, an engineer and president of the Torrance Refinery Action Alliance. “I’m glad about that. But it is evidence, yet again, that accidents happen and that we should not have a dangerous chemical like modified hydrofluoric acid in the inherently dangerous refinery environment in earthquake-prone country.”

Maintenance workers were replacing a small section of flare piping sitting on a rack over a sensitive processing unit when something went wrong about 4:20 p.m. on the east side of the plant near Crenshaw Boulevard, according to refinery and fire officials.

A flash fire broke out just outside the alkylation unit, where modified hydrofluoric acid is used to increase the octane rating of hydrocarbons, said Torrance Fire Chief Martin Serna. Neither the unit nor the acid inside were affected by the accident, he said.

The exact cause has not been determined, but hydrocarbons were still inside the pipe that was removed and Serna said those likely caught fire.

“The refinery fire brigade was able to contain and extinguish the fire with water from the nearby water monitors,” Serna wrote in a statement. “As the fire broke out, the refinery operation personnel shut down the alkylation unit.”

The section of old pipe that had been removed was retained, and its contents will be analyzed by state regulators, he said. Investigators also are looking at “any operational upsets” inside the flare systems prior to the fire.

The flames were extinguished just before 6 p.m. but smoke continued to billow into the air, alarming neighbors already fearful of dangers posed by the refinery. But Torrance City Manager LeRoy Jackson said the incident wasn’t serious, though the dramatic flames and smoke clouds were broadcast on television news stations.

“It was a small fire in the refinery that happened to get on the news,” Jackson said. “Fires happen (at the refinery) from time to time when they’re making changes or modifications to an area.”

PBF Energy spokeswoman Betsy Brien said no one was injured and the refinery’s production continues to meet “our commercial obligations in fuel markets,” indicating that gas prices won’t climb as a result. The plant supplies about 10 percent of the state’s gasoline.

A Feb. 18, 2015, explosion at the refinery, which was then owned by ExxonMobil, rocked the community when an 80,000-pound piece of equipment went flying and crashed within feet of a vessel containing toxic modified hydrofluoric acid.

The damage caused the refinery to shut down for 15 months, resulting in higher gas prices for consumers.

Since then, several groups of community activists have pushed for the refinery to stop using modified hydrofluoric acid, which can form deadly clouds of hard-to-contain toxic gas if released.

“The refinery holds 250,000 pounds of modified hydrofluoric acid. The Department of Homeland Security calls it a chemical of interest for terrorist use in amounts over 1,000 pounds,” Hayati said. “This is a risk too great.”

PBF Energy took over the site from ExxonMobil in July, shortly after the company restarted the plant following the 2015 explosion. Two weeks later, PBF temporarily shut down following a software update that led to a series of equipment failures.

The South Coast Air Quality Management District, Torrance Fire Department, California Division of Occupational Safety and Health and refinery officials continued to investigate Tuesday’s fire and any potential environmental impacts.

The AQMD cracked down on the plant in October for having excessive flaring resulting from power outages and other sudden operational shutdowns. Flares are used to minimize environmental damage caused by the release of hazardous waste chemicals into the air, but the agency said the plant used emergency flares too many times from July through October, and issued several violations demanding corrective actions.

“The bottom line is that we’re seeking a solution to reduce and minimize the flaring that has resulted from the refinery’s power outages because there have been several incidents,” said AQMD spokesman Sam Atwood. “In the end, what we’re seeking is the (administrative law) hearing board to issue an order that will set out specific conditions with the aim of reducing flaring.”

The AQMD also is investigating whether Tuesday’s fire caused any violations of air quality regulations.